Preparation, characterization and thermal-hydrodynamic characteristics of micro-encapsulated phase change suspensions: experimental and numerical study

Circulating cooling water systems have widely used in industrial and civil air conditioning, transferring heat by sensible heat in central air conditioning. However, the low energy storage density results in large temperature rises and low heat transport capacity, leading to high condensing temperatures for refrigerants, which limits the coefficient of performance and degrades cooling efficiency. Herein, this study proposes using micro-encapsulated phase change material suspension (MPCS) with high energy storage density as an alternative coolant to enhance the heat transfer capability. In this study, micro-encapsulated phase change materials was firstly synthesized, and then MPCS at 4, 6, and 8 wt% concentrations was prepared. Their thermal and hydrodynamic performances were systematically evaluated, respectively. After 1000 pumping cycles, 6 wt% MPCS showed a slightly wider particle size distribution (average diameter 674.63 nm), but maintained intact spherical morphology without agglomeration or rupture, demonstrating favourable pumping durability. Furthermore, convective heat transfer experiments were conducted in smooth tubes and tubes with vortex generators using water, 4 wt% and 8 wt% MPCS. At 0.3 m/s, the Nusselt numbers of 4 wt% and 8 wt% MPCS reached 101.9% and 78.6% of water in smooth tubes, while 4 wt% MPCS achieved 106.1% in the tubes with vortex generators. Experimental and numerical investigation demonstrate that the 4 wt% MPCS achieves good heat-transfer performance in vortex-generator-fitted circular tubes relative to smooth circular tubes. This work offers theoretical foundations for MPCS serving as coolants in circulating cooling systems.